Biology subjects

Kollar, L. M.

Publications and source records attributed to Kollar, L. M..

3 recordsLinked to original sources

bioRxiv2024

Testing for the genomic footprint of conflict between life stages in an angiosperm and a moss species

The maintenance of genetic variation by balancing selection is of considerable interest to evolutionary biologists. An important but understudied potential driver of balancing selection is antagonistic pleiotropy between diploid and haploid stages of the plant life cycle. Despite sharing a common genome, sporophytes (2n) and gametophytes (n) may undergo differential or even opposing selection. Theoretical work suggests the antagonistic pleiotropy between life stages can generate balancing selection and maintain genetic variation. Despite the potential for far-reaching consequences of gametophytic selection, empirical tests of its pleiotropic effects (neutral, synergistic, or antagonistic) on sporophytes are generally lacking. Here, we examined the population genomic signals of selection across life stages in the angiosperm Rumex hastatulus and the moss Ceratodon purpureus. We compared gene expression among life stages and between sexes, combined with neutral diversity statistics and the analysis of the distribution of fitness effects. In contrast to what would be predicted under balancing selection due to antagonistic pleiotropy, we found that unbiased genes between life stages were under stronger purifying selection, likely explained by a predominance of synergistic pleiotropy between life stages and strong purifying selection on broadly expressed genes. In addition, we found that 30% of candidate genes under balancing selection in R. hastatulus were located within inversion polymorphisms. Our findings provide novel insights into the genome-wide characteristics and consequences of plant gametophytic selection. SignificanceThe genome-wide importance of balancing selection has been a key question in evolutionary biology. Despite theoretical support for the potential of balancing selection generated by antagonistic pleiotropy between plant life stages, to our knowledge no empirical studies have systematically investigated this on a genome-wide scale. Our results revealed genome-wide patterns more consistent with synergistic pleiotropy, with gametophyte-biased genes more likely to be under relaxed purifying selection in both the angiosperm and moss species we investigated. In addition, our study suggests gene expression level and breadth has a greater effect on selection efficacy than differences between ploidy levels in different life stages.

evolutionary biology↗

bioRxiv2023

The role of breakpoint mutations, supergene effects, and ancient nested rearrangements in the evolution of adaptive chromosome inversions in the yellow monkey flower, Mimulus guttatus

Chromosomal inversion polymorphisms are ubiquitous across the diversity of diploid organisms and play a significant role in the evolution of adaptations in those species. Inversions are thought to operate as supergenes by trapping adaptive alleles at multiple linked loci through the suppression of recombination. While there is now considerable support for the supergene mechanism of inversion evolution, the extent to which inversions trap pre-existing adaptive genetic variation versus accumulate new adaptive variants over time remains unclear. In this study, we report new insights into the evolutionary dynamics of a locally adaptive chromosomal inversion polymorphism (inv_chr8A), which contributes to the evolutionary divergence between coastal perennial and inland annual ecotypes of the yellow monkeyflower, Mimulus guttatus. This research was enabled by the sequencing, assembly, and annotation of new annual and perennial genomes of M. guttatus using Oxford Nanopore long-read sequencing technology. In addition to the adaptive inv_chr8A inversion, we identified three other large inversion polymorphisms, including a previously unknown large inversion (inv_chr8B) nested within the inv_chr8A. Through population genomic analyses and comparative genomics, we determined that the nested inv_chr8B inversion is significantly older than the larger chromosomal inversion in which it resides. We also evaluated key candidate genes involved in gibberellin biosynthesis and anthocyanin regulation, which we hypothesize to underlie the adaptive phenotypic effects of the inv_chr8A inversion. Although little evidence was found to suggest that inversion breakpoint mutations drive adaptive phenotypic effects, our findings support the supergene mechanism of adaptive evolution as a dynamic and continuous process.

genomics↗

bioRxiv2020

Chromosome fusions shape an ancient UV sex chromosome system

Non-recombining sex chromosomes, like the mammalian Y, often lose genes and accumulate transposable elements, a process termed degeneration1,2. The correlation between suppressed recombination and degeneration is clear in animal XY systems1,2, but the absence of recombination is confounded with other asymmetries between the X and Y. In contrast, UV sex chromosomes, like those found in bryophytes, experience symmetrical population genetic conditions3,4. Here we test for degeneration in the bryophyte UV sex chromosome system through genomic comparisons with new female and male chromosome-scale reference genomes of the moss Ceratodon purpureus. We show that the moss sex chromosomes evolved over 300 million years ago and expanded via two chromosomal fusions. Although the sex chromosomes show signs of weaker purifying selection than autosomes, we find suppressed recombination alone is insufficient to drive gene loss on sex-specific chromosomes. Instead, the U and V sex chromosomes harbor thousands of broadly-expressed genes, including numerous key regulators of sexual development across land plants.

evolutionary biology↗